A semiconductor device (1001) includes: a memory cell; and a writing control circuit (107), wherein the memory cell includes a memory transistor (10A) which has an active layer (7A), the active layer (7A) including a metal oxide, the memory transistor (10A) is a transistor which is capable of being irreversibly changed from a semiconductor state where a drain current Ids depends on a gate-source voltage Vgs to a resistor state where the drain current Ids does not depend on the gate-source voltage Vgs, and the writing control circuit (107) is configured to control voltages applied to a drain electrode, a source electrode and a gate electrode such that Vgs≧Vds+Vth is satisfied where Vth is a threshold voltage of the memory transistor (10A) and Vds is a drain-source voltage of the memory transistor (10A), whereby writing in the memory transistor (10A) is performed.