Stefano Brizzi, 50, strangled the PC during a bondage sex session and tried to dispose of the body in an acid bath.
Following an Old Bailey trial, the former Morgan Stanley IT developer was found guilty of murder by a majority of 10 to two after the jury had deliberated for more than 30 hours.
Brizzi, who gave no reaction as the jury delivered its verdict, will be sentenced on Friday December 9.
The court heard how the defendant met his victim on gay dating app Grindr and the met at his flat near London's Tate Modern gallery on April 1.
According to Brizzi, PC Semple died when a dog leash he had been wearing slipped.
But a pathologist concluded that while strangulation was a possible cause of death, it would have taken minutes rather than moments, as the defendant had claimed.
In the days after the killing, crystal meth addict Brizzi was caught on CCTV buying buckets, a perforated metal sheet and cleaning products from a DIY store. He then set about dismembering the body and stripping the flesh.
Brizzi was raised in a strict Catholic family in his native Italy. He said his family's reaction to him coming out as gay led to him abandoning the faith.
The Old Bailey heard how his interest in the darker side of religion surfaced during his visits to Crystal Meth Anonymous as he talked about liking the Devil and satanic imagery.
When police searched his flat in April they found a copy of a book called the Satanic Bible.
But Brizzi insisted that he had not read the book which was written in the 1960s by a man who claimed to be the founder of the Church of Satan.
Following his arrest his uncle Fr Don Piero Sabatini, a parish priest, told Italian media: "May God help him! I can only pray for him, for his soul and for his family."
