Apple has not infringed patents belonging to HTC's S3 Graphics unit, according to the US International Trade Commission (ITC).
The decision marks yet another victory for Apple against HTC, after the ITC ruled in October that Apple's iPhone had not used intellectual property belonging to the Taiwanese firm.
Additionally, also in October, the ITC banned certain HTC devices after Apple accused HTC of patent infringement.
The latest patent dispute with S3 concerned image compression technology.
In July, the ITC said Apple had infringed two of S3's patents but now this decision has been reversed. The ITC said the investigation has now been terminated.
Intellectual property analyst Florian Mueller said he had expected the ITC would not find Apple guilty of infringing S3's patents.
"I think HTC was hoping to reach a point at which Apple was willing to cross licence patents with HTC," Mueller told V3.
"HTC probably thought buying S3 would give them leverage to fight Apple in patent suits but this has not happened."
Mueller said he expected the dispute between Apple and HTC to continue for "quite some time".
"This particular decision comes after a year-and-a-half dispute, and it is not the only lawsuit going on between the two firms," he said.
"HTC and Apple are fighting each other in different countries and with different lawsuits, and final decisions on every case takes a while."
"This is now the best possible outcome for Apple," said Mueller in a blog post. "It's a setback for HTC, which is in the process of acquiring S3 Graphics and was hoping to gain leverage against Apple."
HTC acquired the S3 Graphics division from Via Technologies in July for $300m.
Despite Apple's latest legal victory over HTC, the firm is locked in several ongoing patent disagreements with Samsung.
However, so far Apple is coming out on top, with Samsung suffering losses in Germany and Australia where the Galaxy Tab 10.1 has been temporarily banned, as well as in the Netherlands where the Galaxy S series phones have been temporarily banned.
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