Western Australian Premier Mark McGowan has accused his predecessor Colin Barnett of being bitter and acting without grace or dignity, likening his behaviour in parliament to former federal leaders Mark Latham and Tony Abbott.

In his first speech as a backbencher, Mr Barnett told parliament on Thursday that all the "preconditions" exist for another WA Inc scandal under the new Labor government.

Premier Colin Barnett gets the boot after eight years leading WA.

Mr McGowan said on Friday that he had deliberately left Mr Barnett alone since the election, but the former premier's speech showed "an element of bitterness and lack of reality" that the member for Cottesloe had not dealt with.

"I thought it was sad the way Mr Barnett conducted himself," Mr McGowan told reporters.