fet parameterts
saturn,
A depletion mode junction FET is ON with Vgs = 0. Under this condition, the drain current is relatively independent of the Drain-Source voltage.
This is the Idss.
Idss is not a measure of quality. It is a measure of the maximum current that you can expect the FET to support.
Vgs, or Vgsoff is the magnitude of Gate-to-Source voltage that is required to turn the FET OFF. It is given for a maximum Drain current, e.g., 200uA, and a specified Drain-to-Source voltage, e.g., 10V. For an N-channel depletion mode junction FET, Vgsoff is negative; for a P-channel FET, it is positive. Vgs is not a measure of quality.
For a given family of FETs, the higher the Vgsoff is, the higher will be the Idss.
For a given family of FETs, the higher the Idss value, the lower will be the rdson (drain-to source resistance). The rdson parameter is usually only specified for FETS that are intended for switching applications.
Regards,
Kral