# Power consumption of MOSFET

If I use a P channel MOSFET as a switch for a battery 9v 0.5Ah controlled by an external power source 12 volt will battery last its shelf time if MOSFET is by off?

Update: I dont mind the leakage of the external power supply.

You always get some leakage current. Read the datasheet for that device and look for "$I_{DSS}$" which is known, in their datasheet, as the "Zero Gate Voltage Drain Current".