Photoluminescence (PL) from single silicon quantum dots-nanocrystals (NCs) has been detected and spectrally resolved at room temperature. The Si-NCs, fabricated using electron-beam lithography, reactive ion etching, and two-step oxidation are organized in a regular matrix which enable for repeated observation of a specific single NC. The PL spectrum of a single-NC is formed by a broad band (FWHM of 120 meV or more), in which a quasi-periodic modulation (period of ∼80 meV) appears for some NCs. The emission is polarized in arbitrary directions suggestive of geometrical differences in shape of NCs. The quantum efficiency of PL has been estimated from both saturated and non-saturated PL signal to reach as much as 35%. However only a few percent from total number of NCs shows detectable PL. Our experiments demonstrate the feasibility of PL spectroscopy of single semiconductor NCs in materials with very low emission rate (indirect band gap semiconductors).