Cooperative spectrum sensing has recently become an important research topic for cognitive radio systems because it solves the hidden terminal problem in single-user spectrum sensing. However, idle cognitive users must consume massive spectrum sensing energy for one operating cognitive user. This characteristic reduces the attraction of the cooperative spectrum sensing technique in practical cognitive radio systems. Therefore, this paper develops a partial spectrum sensing algorithm with decision result prediction (DRP) and decision result modification (DRM) techniques to reduce the cooperative spectrum sensing energy. This study also designs and implements an energy-saving spectrum sensing processor for cognitive radio systems. The proposed cooperative spectrum sensing chip reduces energy consumption by about 64% for one fast Fourier transform (FFT) spectrum sensing calculation. For any given specified spectrum detection time, the proposed chip could also improve the detection performance compared to the traditional FFT spectrum sensing.