Uniform, compact, and thick InGaN layers are grown on Si (111) substrates by plasma-assisted molecular beam epitaxy without any buffer layers at low temperatures of around 320 C. By adjusting the Ga/In flux ratio, InGaN layers with In compositions between 10 and 33% are obtained, providing emission covering the whole visible spectral range. The In composition varies less than 2% over large areas, and the single-crystalline hexagonal InGaN layers have a well-defined epitaxial relationship with the Si substrate. Photoluminescence is observed up to room temperature, opening the prospect for the direct integration of InGaN light-emitting devices with Si technology.