A Monte–Carlo program to investigate electromagnetic shower formation in single crystals for particle energies up to 300 GeV is presented. It is based on the well known EGS4-code for amorphous materials and accounts for coherent radiation and pair production which arise in a crystal. Channeling radiation and crystal field assisted pair production are calculated within the uniform field approximation. The increase of energy loss of channeled electrons due to radiation cooling is also included. Good agreement with the available experimental data can be reported.