Hemalatha, M.Johnson, P.S.Harikrishnan, P.K.2026-02-032025Gulf Journal of Mathematics, 2025, 19, 2, pp. 412-423https://doi.org/10.56947/gjom.v19i2.2803https://idr.nitk.ac.in/handle/123456789/20319In this paper, structural properties of lower semi-frames in separable Hilbert spaces are explored with a focus on transformations under linear operators (may be unbounded). Also, the direct sum of lower semi-frames, providing necessary and sufficient conditions for the preservation of lower semiframe structure, is examined. © 2025, Canadian University of Dubai. All rights reserved.direct sumlower semi-frameRiesz-Fischer sequenceSemi-frame