An optical semiconductor device (1A, 1B, 1C, 1D, 1E), comprising: a light-emitting layer having a first main surface, a second main surface opposed to the first main surface, and a side surface; a fluorescent layer (4; 4b) provided on the first main surface and containing phosphor particles, the fluorescent layer (4; 4b) having a third main surface facing the first main surface and a fourth main surface opposed to the third surface; a light-transmissive layer provided on the fourth main surface of the fluorescent layer (4; 4b) and made of a light-transmissive inorganic material; first (7a, 8a, 11a) and second (7b, 8b, 11b) metal portions formed on the second main surface and configured to cause a current for exciting the light emitting layer to flow through the light emitting layer, when a voltage is applied thereto; a sealing layer provided on the second main surface, the sealing layer having a fifth surface facing the third main surface and a sixth surface opposed to the fifth surface, the sealing layer covering the side surface of the light-emitting layer and sealing in the first (7a, 8a, 11a) and second (7b, 8b, 11b) metal portions while leaving first ends (11a, 11b) thereof exposed to an outside of the sealing layer, and the first metal portion (7a, 8a, 11a) comprises a first electrode provided on the second main surface, a first metal post provided on the first electrode and a first metal layer provided on the first metal post, the second metal portion (7b, 8b, 1 1b) comprises a second electrode provided on the second main surface, a second metal post provided on the second electrode and a second metal layer provided on the second metal post, the first metal layer and the second metal layer form the first ends (11a, 11b), and the first ends (11a, 11b) are left exposed at the sixth surface of the sealing layer. a light-emitting layer having a first main surface, a second main surface opposed to the first main surface, and a side surface; a fluorescent layer (4; 4b) provided on the first main surface and containing phosphor particles, the fluorescent layer (4; 4b) having a third main surface facing the first main surface and a fourth main surface opposed to the third surface; a light-transmissive layer provided on the fourth main surface of the fluorescent layer (4; 4b) and made of a light-transmissive inorganic material; first (7a, 8a, 11a) and second (7b, 8b, 11b) metal portions formed on the second main surface and configured to cause a current for exciting the light emitting layer to flow through the light emitting layer, when a voltage is applied thereto; a sealing layer provided on the second main surface, the sealing layer having a fifth surface facing the third main surface and a sixth surface opposed to the fifth surface, the sealing layer covering the side surface of the light-emitting layer and sealing in the first (7a, 8a, 11a) and second (7b, 8b, 11b) metal portions while leaving first ends (11a, 11b) thereof exposed to an outside of the sealing layer, and the first metal portion (7a, 8a, 11a) comprises a first electrode provided on the second main surface, a first metal post provided on the first electrode and a first metal layer provided on the first metal post, the second metal portion (7b, 8b, 1 1b) comprises a second electrode provided on the second main surface, a second metal post provided on the second electrode and a second metal layer provided on the second metal post, the first metal layer and the second metal layer form the first ends (11a, 11b), and the first ends (11a, 11b) are left exposed at the sixth surface of the sealing layer.