Single-event effect (SEE) and total ionizing dose effect (TID) characterization of an 8 Gbps transmitter is investigated in the heavy ion and Co60 experiments. Source-series-terminated (SST) transmitter with T-coil and 3-tap feed-forward equalization (FFE) is adopted in the design and fabricated in a 28 nm commercial bulk CMOS technology. Single-event transient (SET) and single-event function interruption (SEFI) were observed in the heavy ion experiment, but the deterministic jitter (DJ) and random jitter (RJ) of the eye diagram were almost unchanged after 1.2 Mrad(Si) Co60 irradiation. The experimental results indicate that SEE is significant in the transmitter, and SET and SEFI need to be mitigated. While the TID effects are almost negligible, showing minor changes in the deterministic jitter. The most sensitive regions of SEEs are further identified by the pulsed laser experiment for the transmitter, which provides useful information for SEE-hardened design.