On-chip optical light sources are key components in photonic integrated circuits and optical communication. In this paper, we use a novel integration technique called template-assisted selective epitaxy (TASE) to monolithically integrate InP microdisk lasers on silicon. TASE offers several advantages for new device concepts such as lateral doping, dense co-integration of different III-V materials, and in-plane integration with silicon electronics and passive components. Here, we demonstrate room-temperature lasing from InP hexagonal microdisks integrated via TASE. In order to assess and evaluate the viability of TASE, a second InP hexagonal microdisk sample is prepared for comparison using the highly developed and mature direct wafer bonding technique. The lasing performance of the TASE monolithic devices and the bonded microdisk devices is investigated under pulsed optical pumping as a function of temperature and compared. The lasing threshold as well as the light-in light-out curves of our TASE structures compare favorably with the bonded InP hexagonal microdisks. This demonstrates that our TASE approach is a promising technique for the monolithic integration of optical devices on Si.