1. Semi-automatic transmission control system for multi-step gear transmissions, especially for heavy goods vehicles, having a gear lever (2) for engaging the gears, a gear sensor (21) for identifying the gear engaged and for electronically encoding this gear, and having an evaluator circuit (3) which effects the servo-assisted engagement of the gears in the transmission, and having a locking device (1) for the gear lever (2), characterised by the following features : a) a gear position indicator (7) for monitoring the gear changing, b) a sensor (8) for picking up the transmission output speed, c) an electronic unit (4), assigned to the evaluator circuit (3), of which the inputs (9, 10) receive signals relating to the drive condition by means of the gear position indicator (7) and the sensor (8) and of which the output (11) operates the locking device (1) when the output signals of the gear sensor (21) and the sensor (8) correspond to a motor speed that lies outside an optimum motor speed range predetermined by the electronic unit, the locking device (1) holding the gear lever in a gear position determined by the electronic unit (4) and the optimum gear assigned to that gear position being engaged.