Thai police say Ronnakorn Romruen, a local man, has been arrested on suspicion of approaching and attacking the woman while she was travelling on her rental motorbike.
The 23-year-old has been charged with murder, rape and concealing a body, an investigator at Chonburi police station, Somkid Kaensa, said.
Police said the suspect, who operates a trash collecting boat, admitted to the crimes and said he used drugs before the incident.
The body of the 27-year-old tourist with injuries to her head and legs was found on Sunday, hidden under rocks and a pile of leaves.
Koh Si Chang is a popular weekend tourist destination for both locals and foreigners with a population of only 5,000 people.
The island is in Chonburi province, about 40 miles (64km) south of Bangkok.
Mr Somkid said a Thai tourist called police after they saw Mr Ronnakorn's clothes covered in blood. Police then searched the area and discovered the tourist's body.
The investigator said a flower vendor who knew Mr Ronnakorn also saw his clothes were covered in blood and asked him what he was doing.
Mr Somkid said the vendor identified Mr Ronnakorn for police, who went to his home where they found him and the shirt that was covered in blood.
The maximum punishment for premeditated murder in Thailand is the death penalty.
Additional reporting by Associated Press
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