We demonstrate direct modulation of an InAs/GaAs quantum dot (QD) laser on Si. A Fabry-Pérot QD laser was integrated on Si by an ultraviolet-activated direct bonding method, and a cavity was formed using cleaved facets without HR/AR coatings. The bonded laser was operated under continuous-wave pumping at room temperature with a threshold current of 41 mA and a maximum output power of 30 mW (single facet). Even with such a simple device structure and fabrication process, our bonded laser is directly modulated using a 10 Gbps non-return-to-zero signal with an extinction ratio of 1.9 dB at room temperature. Furthermore, 6 Gbps modulation with an extinction ratio of 4.5 dB is achieved at temperatures up to 60 °C without any current or voltage adjustment. These results of device performances indicate an encouraging demonstration on III-V QD lasers on Si for the applications of the photonic integrated circuits.