Kieran Woods scored 13 point to lead Chicago State (4-16, 0-4), which has lost seven straight.
The Aggies had a 17-14 lead midway through the first half, and used a 26-12 surge to stretch it to 43-26 at halftime. Siakam scored 10 points and Sidy Ndir had seven during the span.
Fred Sims Jr. scored five straight points to pull the Cougars to 47-35. Ian Baker made a 3-pointer to spark a 19-6 run to stretch the Aggies' lead to 66-41 with nine minutes and New Mexico State cruised from there.