Conductance of ultrathin polycrystalline silicon wire was measured and periodic plateaus, which provide evidence of the Coulomb staircase at room temperature, are observed. This shows that single‐electron charging effects are important to transport in a semiconductor system at room temperature. The very small (∼10‐nm diam) silicon‐grain structure is presumably playing a key role in creating the observed effects. From the temperature dependence, the electron transport is clearly dominated by the thermal emission, whose activation energy is more than 400 meV. This reveals that the treatment beyond well‐established single‐electron tunneling, including thermal‐emission transfer, is essential to understand such high‐temperature charging effects in semiconductor systems. ©1995 American Institute of Physics.