We present on-chip detection from directly modulated microring quantum-dot (QD) lasers grown on exact (001) Si. Static and dynamic properties of the QD-based microring lasers and microdetectors have been investigated. The ring lasers exhibit high temperature stabilities up to 100± C, low thresholds down to sub milliamp, and a wide 3 dB bandwidth up to 6.5 GHz. The microdetectors show small dark currents down to 0.2 nA and eye openings up to 10 Gbit/s with non-return-to-zero signals. Light emission from the microring lasers can be probed via the changes in the photocurrent of the microdetectors, realizing on-chip QD laser and detector system on Si by epitaxy. Furthermore, demonstrated downscaling abilities of the QD based devices promise improved integration density for photonic integrated circuits (PIC).