American world number one Williams – a six-time champion in Miami and the 2013 winner – cruised past German fifth seed Angelique Kerber 6-2 6-2.
Williams served seven aces and only faced one break point as she crushed the helpless Kerber in just 63 minutes at the WTA Premier event played on hard courts.
Kerber only won 11 points on the Williams serve throughout the contest as the 17-time grand slam champion broke four times for a fourth win in five against Kerber.
The quarter-final wins mean 2014 will be the 14th straight year either a Williams – Serena or sister Venus – or Sharapova have featured in the Miami decider.
Sharapova, runner-up the past three years and five times in total, comfortably beat Czech eighth seed Petra Kvitova 7-5 6-1.
The Russian fourth seed needs to overcome a dreadful record against Williams, who has won 14 straight meetings between the pair and holds a 15-2 head-to-head.
"It's no secret that she's been a big challenge of mine, an opponent that obviously I would love to beat," Sharapova said.
"There are certainly ways I need to step up in certain situations I haven't been able to do in the past against her, but it's great I have the opportunity to play her again."