Difference methods for the solution of the semiconductor flow-equations are discussed. It is shown that implicit schemes are best suited for the particular problem. The successive under-relaxation method (SUR) is appropriate for the solution of the implicit equations. Emphasis is placed on the discussion of the computer-code SECUNDA and its applications in a technical development project. Graphical output and computer animation are powerful resultevaluation techniques. Results for the MESFET and for Gunn diodes show the power and flexibility of the approach presented. © 1972.