Wagering game having a ramping bonus feature

1 . A gaming machine comprising:

a wager-input device for receiving a wager from a player to play a wagering game having a basic game and a bonus game, wherein in response to the wager being at least as large as a threshold amount, a hidden trigger for randomly triggering the bonus game is enabled;

a display for displaying symbols during the basic game, the symbols indicating a randomly selected outcome selected from a plurality of outcomes in response to the wager, the plurality of outcomes including at least one bonus-game-triggering outcome for triggering the bonus game; and

wherein a probability of randomly triggering the bonus game via the hidden trigger is related to an amount of the wager.

2 . The gaming machine of claim 1 , wherein in response to the at least one bonus-game-triggering outcome being achieved and the hidden trigger triggering the bonus game on the same wager, an enhanced bonus is awarded to the player.

3 . The gaming machine of claim 2 , wherein the enhanced bonus is successive plays of the bonus game.

4 . The gaming machine of claim 1 , wherein the threshold amount is two credits per line.

5 . The gaming machine of claim 1 , wherein the probability of triggering the bonus game via the hidden trigger increases as the amount of the wager increases.

6 . The gaming machine of claim 1 , wherein the randomly-selected outcome is selected based on a first random-number generator event, and the hidden trigger randomly triggers the bonus game based on a second random-number generator event.

7 . A method of conducting a wagering game on a gaming machine, the method comprising:

receiving a wager from a player to play the wagering game, the wagering game having a basic game and a bonus game;

randomly selecting a game outcome from a plurality of outcomes in response to the wager;

enabling, in response to the wager being at least as large as a threshold amount, a hidden trigger for randomly triggering the bonus game, a probability of randomly triggering the bonus game via the hidden trigger being related to an amount of the wager;

displaying the game outcome for the wagering game as symbols indicating a randomly selected outcome selected from a plurality of outcomes, wherein the plurality of outcomes includes at least one bonus-game-triggering outcome for triggering the bonus game; and

activating the bonus game if the bonus-game-triggering event is achieved or if the hidden trigger randomly triggers the bonus game.

8 . The method of claim 7 , further including awarding an enhanced bonus to the player in response to the at least one bonus-game-triggering outcome being achieved and the hidden trigger triggering the bonus game on the same wager.

9 . The method of claim 8 , wherein the enhanced bonus is successive plays of the bonus game.

10 . The method of claim 7 , wherein the threshold amount is two credits per line.

11 . The method of claim 7 , wherein the probability of triggering the bonus game via the hidden trigger increases as the amount of the wager increases.

12 . The method of claim 7 , wherein the randomly selecting of the game outcome is based on a first random-number generator event, and the hidden trigger triggers the bonus game based on a second random-number generator event.

13 . A computer readable storage medium encoded with instructions for directing a gaming device to perform the method of claim 7 .

14 . A gaming system for playing a wagering game having a basic game have a standard bonus game, comprising:

at least one display; and

a controller coupled to the display and programmed to

initiate the wagering game in response to detection of a wager from a player, wherein a basic game of the wagering game displays symbols indicating a randomly selected outcome selected from a plurality of outcomes based on a first random-number generator event, the plurality of outcomes including at least one bonus-game-triggering outcome for triggering a bonus game; and

enabling, in response to the wager being at least as large as a threshold amount, a hidden trigger to randomly trigger the bonus game based on a second random-number generator event, a probability of triggering the bonus game by the hidden trigger being related to an amount of the wager.

15 . The gaming system of claim 14 , wherein the display and the controller are both located within a gaming terminal.

16 . The gaming system of claim 14 , wherein the display is located within a gaming terminal and the controller is located outside of the gaming terminal.

17 . The gaming system of claim 14 , wherein the probability of triggering the bonus game via the hidden trigger increases as the amount of the wager increases.

18 . The gaming system of claim 14 , wherein in response to the at least one bonus-game-triggering outcome being achieved and the hidden trigger triggering the bonus game on the same wager, an enhanced bonus is awarded to the player.

19 . A method of playing a wagering game having a basic game and a bonus game that is triggered by an outcome in the basic game, comprising:

receiving from a player a first wager amount, a second wager amount, or a third wager amount for playing the wagering game, the third wager amount being larger than the second wager amount, and the second wager amount being larger than the first wager amount;

in response to the first wager amount being received, playing the basic game;

in response to the second wager amount being received, playing the basic game and independently conducting a random selection with a hidden trigger that triggers a free play of the bonus game, the hidden trigger awarding the bonus game at a first probability; and

in response to the third wager amount being received, playing the basic game and independently conducting the random selection with the hidden trigger, the hidden trigger awarding the bonus game at a second probability.

20 . The method of claim 19 , wherein the second probability is greater than the first probability.