1. Saturation Voltage (Vce(sat)): The CMUT5088E specifies 110mV, while the BC847BT-7-F is 600mV. Under the same 100mA load current, the latter dissipates approximately 5.5 times more power (and generates correspondingly more heat) in the on-state. In switching or low-dropout linear applications, this results in significantly lower efficiency, higher temperature rise, and potential impact on circuit stability. 2. Maximum Power Dissipation (Pd): The CMUT5088E is rated for 350mW, compared to 150mW for the BC847BT-7-F. The former offers superior thermal handling and power capability. If the original circuit operates near the CMUT5088E's power limit, substitution will likely cause failure due to overheating. 3. DC Current Gain (hFE): The CMUT5088E has a minimum gain of 430 at 100µA, whereas the BC847BT-7-F specifies a minimum of 200 at 2mA. This indicates the CMUT5088E provides better weak-signal amplification and higher gain margin in micro-current or high-gain amplifier applications. The lower gain and different test condition of the BC847BT-7-F may lead to insufficient circuit gain if directly swapped. 4. Collector Cut-off Current (ICBO): The CMUT5088E is 50nA, and the BC847BT-7-F is 15nA. While the latter has a better (lower) value, the former remains in the nanoampere range, making its practical impact minimal. The primary difference lies in the breakdown voltage (50V vs. 45V). If the circuit operating voltage or voltage spikes approach 45V, the BC847BT-7-F carries a risk of breakdown. 5. Package Thermal Performance: Although both are nominally SOT-523 packages, the CMUT5088E's notation "SC-89, SOT-490" may imply subtle differences in the internal leadframe or die attach compared to the BC847BT-7-F's "SOT-523." Combined with its higher Pd rating, this suggests the CMUT5088E likely has lower actual thermal resistance and a more robust thermal design.