The spin-orbit interaction in a solid couples the spin of an electron to its momentum. This coupling gives rise to mutual conversion between spin and charge currents: the direct and inverse spin-Hall effects, providing a route for electric generation and detection of spin currents. However, so far, the spin-Hall effects have only been accessible in limited materials, excluding a wide range of indirect-bandgap semiconductors, which precludes further development. Notable in this group is Si, the most fundamental material in the current electronic chips; Si is the key material for seamless integration of spintronics with the current electronics technology. Despite this promise, accessing the spin-Hall effects in Si has been believed to be difficult because of the very weak spin-orbit interaction. Here, we report successful observation of the inverse spin-Hall effect in Si at room temperature. The spin/charge current conversion efficiency, the spin-Hall angle, is obtained as 0.00001 for a p-doped Si film, which is several orders of magnitude smaller than that for doped GaAs. In spite of the small spin-Hall angle, we found a clear electric voltage due to the inverse spin-Hall effect in the p-Si film, demonstrating that Si can be used as a spin-current detector.