Some products of Synopsys from ex-Avant! support SMP such as Hspice, Star_RCXt, Hercules.... But You won't get a free luch, it require an extra license for every pairs of CPU use, 1-2 CPUs 1 license, 3-4CPUs 2 licenses, 5-6 CPUs 3 license . For 6 CPUs the performance only increase 3 times. Personnaly, I think that, in simulation case, if your circuit have a lot of feedback, the performance haven't improve much. and Yes, you have to put in a switch at the line comand to tell that you are running multi-threading