Hoskins, who turns 20 next month, moves to The Lamex Stadium as Boro look to push for a play-off place in the latter half of the season.
The forward is currently joint-top of the goalscoring charts in the Barclays U21 Premier League after hitting nine goals for our Under-21s in their first 12 games this season.
That form saw him fire Saints' Development Squad into the Elite Group Stage of the U21 Premier League and has secured him a loan spell in League 1.
Hoskins made a substitute appearance for Saints' First Team against Stevenage earlier this season, playing the final five minutes of our Capital One Cup win at The Lamex Stadium.
The youngster spent the final three months of last season on loan in League 2 with Rotherham United, where he made eight appearances and scored twice.