The etching of silicon in a pulsed plasma using SF6 gas is investigated. For short pulses the Si etch rate for a pulsed plasma is essentially the same as for the continuous plasma, in spite of the duty cycle being only 20%. An heuristic model of the etching has been developed which accurately predicts the pulsed plasma etch rates and sets limits on important parameters, such as the number of F atoms yielded by the SF6, the reaction probability of F with Si, and the overall efficiency of the etching process.