Abstract
The current voltage characteristics of Josephson junctions at finite temperatures under microwave irradiation are simulated in the resistively, capacitively, inductively shunted junction (RCLSJ) model including white noise. The simulated results as function of microwave power clearly show the appearance of Shapiro steps. It is shown that higher steps are suppressed for low microwave amplitudes. The rounding of the Shapiro steps observed experimentally has been reproduced by taking noise into consideration in RCLSJ model.