Abstract: When compound semiconductor films are grown on an InP wafer having a surface near a (100) orientation hillocks tend to arise on the films. Off-angle wafers have been adopted for substrates in order to suppress the occurrence of hillocks. The off-angle .THETA. from a (100) plane, however, is not the sole factor for determing wheather hillocks will be formed on the film. There is a concealed parameter which determines the generation of hillocks. What induces hillocks on the growing film are the defects on the substrate itself. No hillocks originate on portions of the film that correspond to the portions of the InP wafer without dislocations. The role of the off-angle .THETA. of the substrate is preventing the influence of the dislocations from transmitting to the films. A smaller density D of the defects on the substrate allows a smaller off-angle .THETA. for suppressing the hillocks from arising.