In order to examine the difference in the irradiation effects on Si electronic devices between deuterium-tritium (DT) and deuterium-deuterium (DD) fusion neutrons, several types of memory integrated circuits (ICs), charge coupled device (CCD) image sensors and a Si surface barrier detector (Si-SBD) were irradiated with neutrons from a deuteron accelerator. The transient effects (i.e., neutron-induced background noises) and permanent effects (i.e., neutron damage) on them were measured in situ during irradiation. Regarding the transient effects, soft error upsets, brightening spot noises and induced-charge noises were measured for the memory ICs, CCDs and the Si-SBD, respectively. As for the permanent effects, the number of damaged cells of the CCDs and the leakage current of the Si-SBD increased with neutron fluence. We also developed a Monte-Carlo code which used the code TRIM for charged particle transport to evaluate the DT and DD neutron effects on the Si devices. The calculated correlation factor of DT and DD neutron damage for the Si devices agreed approximately with the correlation factor obtained from the irradiation experiments on the CCDs and Si-SBD.