In this paper, optoelectronic characteristics and related switching behavior of one monolithically integrated silicon light-emitting device (LED) with an interesting wavelength range of 400–900 nm are studied. Through the comparison of two types of geometry, Si avalanche-based LED and Si field-effect LED (Si FE LED), in the same device, we establish the dimensional dependence of the switching speed of the LED. Almost-linear modulation curve implies lower distortion is shown for the Si FE LED with light emission enhancement, and technology computer aided design (TCAD) simulations are in line with the experimental results. Our findings indicate that ON–OFF keying up to GHz frequencies should be feasible with such diodes. Potential applications should include Si FE LED integrated into the micro-photonic systems.