Ehibhatiomhan, 20, heads out for his second loan, having spent the first half of the season at Ian Holloway’s Swindon Town.
He scored once in 14 appearances for the League Two side before being recalled by Saints in January to rejoin the under-21s.
Salford currently sit third in England’s fourth tier, with hopes of earning promotion to League One.
“I’m very excited to be here. I spoke to the manager earlier today, and he expressed his interest in how he’s followed me throughout my career,” said Ehibhatiomhan.
“It all sounds really positive, a good group that I can fit into that will get the best out of myself, and hopefully I can contribute as much as I can.”
Karl Robinson added: “Prince is strong, powerful and will bring a real force for us at the top end of the pitch to add to the quality we already have in those positions.
“He is young and determined to make a good impression, and we are looking forward to working with him. I would also like to thank Southampton for allowing Prince to join us for the rest of the season.”