Kelly Brazier added the extra to make it a one-point game.
However, the remainder of the first half belonged to Waikato as they added another three tries.
The first was a brilliant sniping run from halfback Violet Hapi-Wise, who collected the ball from the lineout 60 metres out to run away basically untouched to score in the right corner.
The second of the three saw hooker Grace Houpapa-Barrett with a pick and go close to the line to barge her way over to score her first of three tries for the afternoon.
The final try before the halftime break was scored by first five-eighth Kiriana Nolan, who pounced on a Volcanix mistake to race away to score under the posts.
Semple was successful with two out of the three conversions as Waikato led 27-7 after the first 40 minutes.
In the second half, Houpapa-Barrett made it a brace after another pick and go, close to the line.
Semple could not add the extras as Waikato extended their lead to 25 points after 43 minutes.
Bay of Plenty then scored back-to-back tries to cut Waikato’s lead to just 11 points when Tihore scored her second and Grace Parata-Stewart scored five minutes later.
Brazier added the extras with both conversions as Waikato led 32-21 after 53 minutes.
Approaching the midway point of the second half, Waikato’s Lela Ieremia crossed in the corner, after the Volcanix ran out of numbers down the right-hand side.
Semple was unsuccessful from the sideline as Waikato extended their advantage to 16 points.
Bay of Plenty again closed the gap to 11 points with 10 minutes remaining after Payton Takimoana found a gap in the Waikato line to score.
But with four minutes remaining, Houpapa-Barrett, scored from the back of a driving maul to complete her hat-trick and put the game out of reach for the Volcanix to make a late comeback.
Waikato had done enough to lock in a bonus point 42-26 win.
Reserve halfback Ariana Bayler celebrated a huge milestone, playing her 50th Waikato cap after making her debut in 2013.
Bayler is the third Waikato women’s player to achieve such a feat, joining Victoria Edmonds and Chelsea Semple as the only players to reach this milestone.
Waikato 42 (Montessa Tairakena, Violet Hapi-Wise, Grace Houpapa-Barrett 3, Kiriana Nolan, Lela Ieremia tries; Chelsea Semple 2 conversions, 1 penalty)
Bay of Plenty Volcanix 26 (Jordyn Tihore 2, Grace Parata-Stewart, Payton Takimoana tries; Kelly Brazier 3 conversions)
HT: 27-7