shown in fig4 when the transistor having the structure as shown in fig1 a is used and the dose of impurities in the channel is a certain value it is sufficient to select two gate length values in the region where the leakage currents vthleak decrease even when the threshold increases although the threshold of the transfer mos transistor is lower than that of the drive mos transistor it is sufficient to select a transistor in which vthleak corresponding to the leakage current is equal to or larger than vthleak of the drive mos transistor in this case as the transfer mos transistor a transistor f having a long gate length with the same dose of impurities into the channel as that of the low threshold transistor in the logic circuit can be used in a dram 141 by using a transistor having the same dose of impurities in the channel and the same gate length as those of the transistor f shown in fig1 b and having the thickness of a gate oxide film different from that of the transistor f shown in fig1 b the dram memory cell having suitable characteristics such that the threshold is lowered without increasing the leakage currents can be realized generally the threshold voltage is defined in two ways one is a threshold voltage obtained by extrapolation of a saturation current and the other one is a threshold voltage obtained from a gate voltage for passing a constant current in a region where the gate voltage is sufficiently low the threshold voltage in the invention corresponds to the former one and vthleak corresponds to the latter one although it is written as mosfet in the specification a known misfet can be also used according to the invention as described above.