the mosfet grid acts as acapacitor.
if you don't discharge the grid capacitance, it stays on for a time until leakage current do the job...
the same for igbt's
at least use a bleeder resistor of 1k...
for efficient command of mosfet or egbt you must use a push pull stage to have a fast charge/discharge otherwise the transistor will stay in linear mode and generate a lot heat... in switching mode heat is minimal (full current and minimal voltage across transistor or no current and full voltage)
hope this will help