In this paper, we propose a specific two-layer model consisting of a functionally graded (FG) layer and a piezoelectric semiconductor (PS) layer. Based on the macroscopic theory of PS materials, the effects brought about by the attached FG layer on the piezotronic behaviors of homogeneous n-type PS fibers and PN junctions are investigated. The semi-analytical solutions of the electromechanical fields are obtained by expanding the displacement and carrier concentration variation into power series. Results show that the antisymmetry of the potential and electron concentration distributions in homogeneous n-type PS fibers is destroyed due to the material inhomogeneity of the attached FG layer. In addition, by creating jump discontinuities in the material properties of the FG layer, potential barriers/wells can be produced in the middle of the fiber. Similarly, the potential barrier configuration near the interface of a homogeneous PS PN junction can also be manipulated in this way, which offers a new choice for the design of PN junction based devices.