Why do Toshiba's power MOSFETs exhibit larger gate-source leakage current, IGSS, than those of other companies?

Toshiba's Power MOSFETs generally have a Zener diode between gate and source for electrostatic protection, which contributes additional leakage current to IGSS. Therefore, Power MOSFETs with a Zener diode exhibit a slightly larger IDSS than those without one (which cause leakage current only from a dielectric film).