Are the transistors used as a power switch, or as phase switches?
If you need a lower-loss switch a MOSFET like IRF520 or similar can be used. Its channel resistance is low, but make sure the gate-channel voltage cannot exceed TTL logic limits. I use always a 5.1 Zener across the gate/drain input, and a 10 kOhm resistor from the input to gate to make sure the MOSFET is safe.
Make sure you use a good heat sink as the MOSFET could be hot due to transitions from OFF to ON state.