A method including forming an intermediate product, the intermediate product being configured to include a wiring substrate including a plurality of first electrodes, a plurality of second electrodes and a plurality of test electrodes, a first semiconductor chip mounted over the wiring substrate and including a plurality of first pads electrically connected respectively to the first electrodes, and a second semiconductor chip stacked over the first semiconductor chip and including a plurality of second pads electrically connected respectively to the second electrodes; encapsulating the first and second semiconductor chips; and performing electrical tests on the first and second semiconductor chips by use of the test electrodes, after the encapsulating of the first and second semiconductor chips.