A domestic worker has been jailed for 10 months for having sex with a minor half her age.

The 28-year-old Indonesian woman admitted on Monday to having sex with her employer's 14-year-old son in their house on Sept 5. Neither party can be named due to a gag order.

The court heard that the woman came to Singapore in late June and started working for the boy's family on July 3.

At about 7pm on Sept 5, the boy was at home with the woman and another foreign domestic helper. His parents and his uncle, who lives there, were not at home at the time.

The Secondary 2 student was showing card tricks to the woman when she tried to hug him, but he moved her hand away.

Later, he went up to his room. The woman followed shortly after. He was seated when she approached him from behind and kissed his cheeks and neck.

He stood up and tried to walk to the door.

However, before he could leave, she hugged him and began to undress.

Stunned by what was happening, he did not resist. She then removed his clothes, led him to his bed and had sex with him.

She stopped when she heard the boy's uncle come home.

The boy later told his father what had happened and his mother called the police.

Deputy Public Prosecutor Nicholas Lai cited aggravating factors when he asked the court to impose at least 10 months' jail on the woman.

He said there was breach of trust and a wide age disparity between the parties.

She also had unprotected sex with the boy - which, in itself, was reprehensible - when she had been tested positive for Chlamydia trachomatis, a sexually transmitted disease.

"It could have been sheer luck that the boy was eventually not infected, but the fact remains that she put the boy at risk of being infected, and an adverse inference should be drawn against her,'' he said.

The woman, whose sentence was backdated to Sept 7, could have been jailed for up to 10 years and fined for having sex with a person under 16 years old.