The dc characteristics of the level 1 through level 3 MOSFETs are defined by the device parameters vto, kp, lambda, phi and gamma. These parameters are computed by ngspice if process parameters (nsub, tox, ...) are given, but users specified values always override. vto is positive (negative) for enhancement mode and negative (positive) for depletion mode N-channel (P-channel) devices.

Charge storage is modeled by three constant capacitors, cgso, cgdo, and cgbo, which represent overlap capacitances, by the nonlinear thin-oxide capacitance that is distributed among the gate, source, drain, and bulk regions, and by the nonlinear depletion-layer capacitances for both substrate junctions divided into bottom and periphery, which vary as the mj and mjsw power of junction voltage respectively, and are determined by the parameters cbd, cbs, cj, cjsw, mj, mjsw and pb.

Charge storage effects are modeled by the piecewise linear voltages-dependent capacitance model proposed by Meyer. The thin-oxide charge-storage effects are treated slightly different for the level 1 model. These voltage-dependent capacitances are included only if tox is specified in the input description and they are represented using Meyer's formulation.

There is some overlap among the parameters describing the junctions, e.g. the reverse current can be input either as is (in A) or as js (in (\frac{A}{m^{2}})). Whereas the first is an absolute value the second is multiplied by ad and as to give the reverse current of the drain and source junctions respectively.

This methodology has been chosen since there is no sense in relating always junction characteristics with ad and as entered on the device line; the areas can be defaulted. The same idea applies also to the zero-bias junction capacitances cbd and cbs (in F) on one hand, and cj (in (\frac{F}{m^{2}})) on the other.

The parasitic drain and source series resistance can be expressed as either rd and rs (in ohms) or rsh (in ohms/sq.), the latter being multiplied by the number of squares nrd and nrs input on the device line.