In this work, an optical 8-amplitude phase shift keying (8APSK) modulator has been designed and successfully simulated using three silicon microring modulators (MRMs). The first two MRMs jointly generate a QPSK signal, while the third MRM is connected in an add-drop configuration to synthesize the final 8APSK signal. The MRMs have a junction volume of 4.5×10−12 cm−3 with carrier recombination lifetime of 100×10−12 seconds. We have obtained the simulated constellation plots at various signal-to-noise ratios and achieved a bit error rate of 10−3 at around 10.7 dB optical signal to noise ratio.