You can use silicone sealant instead of caulk to seal your half glass shower wall. However, a few things should be kept in mind before doing so.
Silicone sealant will not adhere as well to glass as caulk will. This means it is more likely to fail and allow water to leak.
Silicone sealant is more difficult to remove than caulk, so if you ever need to replace it, it will be more complex and time-consuming.
Silicone sealant is not as flexible as caulk, so it is more likely to crack over time.