SEMICONDUCTOR DEVICE

PURPOSE:To suppress overshoot noise due to laser diode by feeding ON current to a first transistor while preventing suction of load bias current. CONSTITUTION:After turn ON of a transistor T6 before turn ON of a transistor T3, a transistor T4 in the current supply circuit CS of a laser diode driver LDD is turned ON to feed a predetermined current IC. The current IC is sucked through the transistor T6 being turned ON thus producing a current for perfectly turning the transistor T6 ON. Consequently, a driving current IL corresponding to IB+IA flows constantly through a laser diode LD even during an interval after turn ON of the transistor T6 and before turn ON of the transistor T3. Furthermore, the transistor T6 is fed with sufficient ON current and approaches perfect ON state quickly.