The SP model has been outdated by the PSP model. Documentation on the old SP model can be found below. Documentation on the new PSP model can be found using the links below.
The SP model is a surface-potential based compact MOSFET model. It is produced by Prof. Gennady Gildenblat's SP Modeling Group from the Pennsylvania State University. Send questions, comments, suggestions, etc. to Prof. Gildenblat.