Yes, it certainly is.  Biblically, baptism is WHEN one is forgiven of sins and receives the gift of the Holy Spirit. (Acts 2:38-41).  Acts 22:16 provides further evidence, as Paul is told, “And now, what are you waiting for? Get up and be baptized,  and wash your sins away.  If baptism is when one is saved, then, by definition, it is required for salvation.   It can be compared to marriage.  We become married when we go through a marriage ceremony (or whatever type, as the Bible does not specify how it ought to be done).  Because the ceremony is when we are married, it is, by definition, required in order to be married.   Or we could compare it to signing a contract.  The contract becomes official when it is signed by both parties.  Therefore, the signature is essential for the contract to go into effect, by definition.

If we have not been baptized, then we are not forgiven of our sins or received the gift of the Holy Spirit.  This is taught in the Scriptures.  For example, in Galatians 3:27 Paul reminds us that we are baptized into Christ.  Before baptism we are outside of Christ.  When we are baptized, we come into Christ.  There is no mention anywhere in the entire New Testament of any other connection to coming into Christ than in baptism.  In Romans 6:2-4 we are told that when we are baptized into Christ, we are baptized into his death.  If we have not been baptized into his death, then we will not be joined with him in his resurrection.  This is one of the most obvious and clear teachings in the entire New Testament–that we are baptized into Christ, and therefore, baptism is when we come into Christ and are saved.

John Oakes