We develop a wage-structure determination model in which a firm with incomplete information offers an optimal sequence of contracts for its heterogeneous employees. The model integrating the principal-agent framework and monitoring mechanism is characterized by endogeneity of the selection of two compensation methods: performance-pay and non-performance-pay schemes. The model is used to examine the switching of pay schemes and its inequality effect. We point out that the growth of performance-pay jobs is accompanied by a downward adjustment of the rewards for performance, which brings forth a countervailing effect on wage inequality. The simulation analysis of a case of uniform-distributed ability reveals that the net effect of the growth of performance-pay jobs on wage inequality depends on the driving force behind the switch.