Semiconductor device and its control method

1. A semiconductor device comprising:

sectors having memory cells connected to local word lines;

decoders selecting the sectors; and

a circuit generating, in erasing of a selected sector, a control signal that causes a corresponding one of the decoders associated with the selected sector to be temporarily unselected.

2. The semiconductor device as claimed in claim 1 , wherein:

each of the sectors comprises a pull-up transistor that is driven by a corresponding one of the decoders via a corresponding one of global word lines connecting the sectors and drives one of the local word lines; and

the pull-up transistor is kept OFF by the control signal.

3. The semiconductor device as claimed in claim 1 , wherein the circuit generates the control signal that keeps the corresponding one of the decoders unselected in an initial stage of erasing.

4. The semiconductor device as claimed in claim 1 , wherein the circuit generates the control signal that keeps the corresponding one of the decoders unselected until a negative pump path connected to the corresponding one of the decoders unselected falls to a given intermediate negative voltage in erasing.

5. The semiconductor device as claimed in claim 1 , wherein:

each of the sectors comprises a pull-up transistor and a pull-down transistor for driving one of the local word lines, both transistors being driven by a corresponding one of the decoders; and

the control signal disabling a path including the pull-up and pull-down transistors for a given period of time in erasing.

6. The semiconductor device as claimed in claim 1 , wherein the memory cells are non-volatile memory cells.

7. A method of controlling a semiconductor device comprising the steps of:

selecting one of sectors having memory cells connected to local word lines; and

generating, in erasing of a selected sector, a control signal that causes a decoder for selectively driving the selected sector to be temporarily unselected.