This work compares GaN and Silicon transistors for audio applications. A 200 W Bridge-Tied Load Class-D amplifier which operates from a 40 V single supply has been designed from scratch and built. Such custom amplifier can use either Silicon MOSFETs or GaN Power Transistors. Experimental measures and tests were conducted to fully characterize the amplifier when using alternatively Silicon and GaN transistors. Eventually, laboratory measurements prove GaN devices superior, thanks to their lower parasitic capacitances and switching charges, achieving higher efficiency and lower distortion.