Trump will likely become the party's candidate, facing Joe Biden in November's US Presidential Election.
ADVERTISEMENTDonald Trump has won more Republican primaries, celebrating victories in Michigan, Missouri and Idaho on Saturday.
His overwhelming lead to become the party's presidential candidate has now become even bigger.
In Michigan, the 77-year-old beat Nikki Haley - his last remaining rival in the race - in all 13 districts.
Meanwhile, his victory was pronounced less than two hours after voting started in Missouri.
Trump's wins are another setback for Nikki Haley, a former UN Ambassador.
She vowed to continue at least until the "Super Tuesday", when 15 states will vote simultaneously, distributing more than a third of Republican delegates at once.
In the Virginia capital of Richmond on Saturday, thousands queued for several hours to hear Trump speak. He vowed to "win big" in the next round of voting.
"We got numbers today that were unbelievable," Trump told the crowd.
His speech focused on migration at the US-Mexico border, blaming US President Joe Biden for a supposed crisis at the borders.
The Democrat has, in turn, accused Trump of sabotaging efforts to pass a bipartisan immigration bill that would boost border forces, fund a border wall and fast-track asylum cases.
"Once again Trump is projecting in an attempt to distract the American people from the fact he killed the fairest and toughest border security bill in decades because he believed it would help his campaign," spokesman Ammar Moussa said.
Polls show migration is an issue that resonates strongly with the US electorate, which will likely be a major battleground in the upcoming presidential election.
The winner of the Republican primaries will likely face Biden in November's Presidential election.
A New York Times and Siena poll released on Saturday found that 48% of US voters would back Trump over the Democrat, compared to 43% for the current president.