This name (like the names Spirit of Jesus Christ, Spirit of Jesus, and Spirit of Christ) is a name of the Holy Spirit that reminds us of the unity of the three persons of the Trinity: Father, Son and Holy Spirit.
Spirit of His Son in Greek:
To pneuma tou hyiou autou
Strong’s Concordance numbers: 4151, 5207
Bible reference: Gal. 4:6
Because you are his sons, God sent the Spirit of his Son into our hearts, the Spirit who calls out, “Abba, Father.” (Galatians 4:6 NIV)