In this paper, we propose a novel modulation that combines the spatial modulation (SM) with the subcarrier intensity-modulation (SIM) for optical wireless communications. The performance of SIM-SM scheme is compared to a conventional SIM by computer simulation. For the spectral efficiency (SE) of 2bits/s/Hz, the performance gain about 2dB is achieved. As the SE increases to 3bit or 4bits/s/Hz, the Eb/N0 gain becomes about 5dB. It is shown the attenuation for the SIM is more serious than the SIM-SM according to increasing the number of the subcarriers.