2n6661.pdf datasheet:

Supertex inc.2N6661N-Channel Enhancement-ModeVertical DMOS FETFeaturesGeneral DescriptionThe Supertex 2N6661 is an enhancement-mode (normally- Free from secondary breakdownoff) transistor that utilizes a vertical DMOS structure Low power drive requirementand Supertexs well-proven silicon-gate manufacturing Ease of parallelingprocess. This combination produces a device with the Low CISS and fast switching speedspower handling capabilities of bipolar transistors, and the Excellent thermal stabilityhigh input impedance and positive temperature coefficient Integral source-drain diodeinherent in MOS devices. Characteristic of all MOS High input impedance and high gainstructures, this device is free from thermal runaway and Hi-Rel processing availablethermally-induced secondary breakdown. ApplicationsSupertex