The change came among a series of orders issued by the king yesterday, who shuffled his cabinet and replaced the head of the army which for two years has been fighting rebels in neighbouring Yemen.
"Prince Abdullah bin Faisal bin Turki removed as ambassador to the US. Prince Khaled bin Salman bin Abdulaziz appointed ambassador," the official Saudi Press Agency reported, citing a royal order.
Prince Abdullah had served in the post for just over a year, according to the website of the Saudi embassy in Washington.
But ties between Riyadh and Washington became increasingly frayed during the administration of president Barack Obama.
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Saudi leaders felt Obama was reluctant to get involved in the civil war in Syria and was tilting toward Riyadh's regional rival Iran.
The Saudis have found a more favourable ear in Washington under Trump, who took office in January and has denounced Iran's "harmful influence" in the Middle East.
Washington provides some logistical and intelligence support, as well as weapons, for the Saudi-led coalition in Yemen.
Prince Khaled, the new ambassador, is an air force pilot who flew missions as part of that anti-IS coalition, said Salman al-Ansari, president of the Saudi American Public Relation Affairs Committee (SAPRAC).
Ansari, whose committee is a private initiative to strengthen Saudi-US ties, described Prince Khaled as a "very organised personality, savvy, youthful, and active."
Another son of King Salman, Deputy Crown Prince Mohammed bin Salman, 31, is second in line to the throne and is one of the kingdom's most powerful figures.
US Defence Secretary Jim Mattis visited Riyadh on Wednesday and said it was in Washington's interest "to see a strong Saudi Arabia". He pointed to the kingdom's "military security services and secret services".