Osaka produced a brutal display of power hitting under the roof on Rod Laver Arena, striking 56 winners in a 6-2 4-6 6-4 victory and will face Petra Kvitova on Saturday.
The 21-year-old's achievement makes her the first women to back up a first slam title by making the final of the next major tournament since Jennifer Capriati in 2001.
As well as the title, the world number one ranking will also be on the line on Saturday, with Kvitova and Osaka both looking to get there for the first time.
Capriati followed her maiden title here 18 years ago by winning the French Open and, if Osaka can maintain the form she showed in this match, then there is absolutely no reason why she cannot emulate that.
Having survived tough battles against the unconventional pair of Hsieh Su-wei and Anastasija Sevastova earlier in the tournament, Osaka certainly looked more comfortable taking on a fellow ball-basher.
And bash the ball she did, repeatedly into the corners, off both forehand and backhand, to win the first set.
Osaka had won her previous 58 matches after winning the first set but – following her remarkable comeback to beat Williams – Pliskova would have known that no cause was impossible.
Osaka broke serve again at the start of the second set but then gave it straight back with a poor game and slowly the momentum began to shift, the two women trading fiercer and fiercer blows.
Osaka produced some fine play to hold off her opponent at 3-4 but two games later Pliskova broke to love to take the match to a decider.
The 26-year-old, who reached her only slam final at the US Open in 2016, looked to continue her momentum at the start of the decider but Osaka saved three break points before playing a tremendous return game to move 2-1 ahead.
Pliskova had one chance to get back on level terms in the eighth game but Osaka served an ace, and then another one – given by HawkEye – to clinch the victory.