The replication of various microstructures with an aspect ratio of 5 was studied both experimentally and by numerical simulation, using the microinjection molding process. The microstructures were produced on poly(lactic) acid disks using a steel insert made by micromachining. To improve the filing process, the insert was heated at temperatures above the polymer glass transition temperature of about 60 oC, and then rapidly water-cooled to room temperature. The cavity pressure and the temperature at the gate were monitored during the whole cycle. The results show that the micro features close to the gate did not fill as well as features far from the gate.