Halep, who is the current world No.1, is in reliable form and looking a good bet to pick up her first ever Grand Slam title later this month at the Australia Open.
Halep, 26, made it to the French Open final in 2017 but was beaten to the title by Jelena Ostapenko. She was also knocked out in round one of last year's Grand Slam in Melbourne.
The five-time Grand Slam champion will be playing in her first Australia Open since reaching the quarterfinal stage in 2016.
It was Siniakova who secured the place, beating her countrywoman 6-2, 6-2 to set up a final-four clash against Sharapova