In a silicon wafer, temperature oscillations observed in a thermal chamber of the rapid thermal annealing set up are investigated in the conditions corresponding to a bistable behavior of a wafer. Oscillations with a typical period near ~400 s are observed at temperatures corresponding to the unstable branch of the s-shaped transfer characteristic of the wafer. Temperature behavior of the wafer at the different regimes of heat exchange is analyzed and it is shown that the oscillations depend on the availability of the negative feedback between the wafer and water-cooled pedestal, through which the heat output is released from the wafer. Oscillation excitation mechanism in such a heat system is offered and the theoretic model of the oscillations is derived. Estimations of the oscillation period obtained by the use of the theoretical model fall in the range between 10 3 and 10 4 s.