Merthyr secured their spot by comfortably beating Ystrad Rhondda 10-50 while Beddau had to work harder to earn their berth with a closely fought 16-10 victory over Bonymaen.
Bridgend Athletic brushed aside Penallta 33-0 while Glamorgan Wanderers fought off the challenge of Tondu with a 20-13 win.
Semi Finals of the Webb Ellis Youth Cup:
Beddau Youth v Merthyr Youth
Bridgend Athletic Youth v Glamorgan Wanderers Youth
Quarter Final Results
Ystrad Rhondda Youth 10 Merthyr Youth 50
Penallta Youth 0 Bridgend Athletic Youth 33
Beddau Youth 16 Bonymaen Youth 10
Glamorgan Wanderers Youth 20 Tondu Youth 13