This article estimates the policy reaction function of the Swiss National Bank (SNB) using real‐time internal inflation forecasts and output gap estimates from 2000 to 2012. We analyze potential nonlinearities of policy rate responses to economic fundamentals using a novel semiparametric approach. We find a linear response of the SNB's policy rate to inflation forecasts but a strong nonlinear response of the policy rate to the output gap and exchange rate changes. This finding suggests that the SNB reacts to extreme movements of these variables if they become a concern for price stability and economic activity.