A matrix is formed using a plurality of memory cells in each of which a drain of the writing transistor is connected to a gate of a reading transistor and one electrode of a capacitor. A gate of the writing transistor, a source of the writing transistor, a source of the reading transistor, and a drain of the reading transistor are connected to a writing word line, a writing bit line, a reading bit line, and a bias line, respectively. The other electrode of the capacitor is connected to a reading word line. In order to decrease the number of wirings, the writing bit line is substituted for the reading bit line. The reading bit line is formed so as to be embedded in a groove-like opening formed over a substrate.