Amorphous carbon film (a-C film) was deposited on n-Si substrate by pulsed-laser deposition at room temperature. The electrical transport properties of a-C film/n-Si were investigated by current–voltage (I–V) measurements at various temperatures. The results indicate that the resistance of a-C film/n-Si is controlled by the applied electric current. The most important result is that when the value of the electric voltage is larger than a threshold, the current increases abruptly to a very large value, and the value of the voltage threshold decreases with increasing temperature. Correspondingly, the colossal electroresistance (ER) was achieved in the temperature range measured. The ER reaches −84.5% and −99.5% at T=310K and 170K, respectively. The mechanism of the I–V characteristics may be understood by an energy band structure of a-C film/n-Si. The anomalous I–V characteristics and colossal ER should be of interest for various applications such as field-effect devices.