MOSFET models are the central part of ngspice, probably because they are the most widely used devices in the electronics world. Ngspice provides all the MOSFETs implemented in the original Spice3f and adds several models developed by UC Berkeley's Device Group and other independent groups.

Each model is invoked with a .model card. A minimal version is:

.model MOSN NMOS level=8 version=3.3.0

The model name MOSN corresponds to the model name in the instance card (see 11.1). Parameter NMOS selects an n-channel device, PMOS would point to a p-channel transistor. The level and version parameters select the specific model. Further model parameters are optional and replace ngspice default values. Due to the large number of parameters (more than 100 for modern models), model cards may be stored in extra files and loaded into the netlist by the .include (2.6) command. Model cards are specific for a an IC manufacturing process and are typically provided by the IC foundry. Some generic parameter sets, not linked to a specific process, are made available by the model developers, e.g. UC Berkeley's Device Group for BSIM4 and BSIMSOI.

Ngspice provides several MOSFET device models, which differ in the formulation of the I-V characteristic, and are of varying complexity. Models available are listed in table 11.1. Current models for IC design are BSIM3 (11.2.10, down to channel length of 0.25 µm), BSIM4 (11.2.11, below 0.25 µm), BSIMSOI (11.2.13, silicon-on-insulator devices), HiSIM2 and HiSIM_HV (11.2.15, surface potential models for standard and high voltage/high power MOS devices).

Table 11.1: MOSFET model summary