South Korea's top tech giant Samsung Electronics Co. is expected to post weaker-than-expected earnings for the third quarter of 2015, analysts said Monday, due to the delayed recovery of its handset business.

Samsung Electronics is expected to post an operating profit of 6.5 trillion won ($5.5 billion) in the July-September period, Korea Investment & Securities Co. said in a note to investors. The figure hovers below the 6.6 trillion won average outlook compiled by Yonhap Infomax, the financial arm of Yonhap News Agency, from 22 local brokerage houses.

In the second quarter, Samsung posted an operating profit of 6.89 trillion won, down 4.03 percent on-year.

Korea Investment said the weaker outlook is due to expectations that the mobile business will suffer a decline in earnings despite improved shipments as the portion of high-end devices is falling.

The combined shipments of smartphones is estimated at 81 million units in the July-September period, up 12.5 percent on-quarter. The operating profit from the mobile arm, however, is estimated at 2 trillion won, down 26.5 percent.

The increase in the marketing costs amid the release of new devices, such as the Galaxy Note 5, will also emerge as a drag on third-quarter earnings, the brokerage added.

Samsung has been facing challenges in its handset sales due to the rise of Chinese rivals rolling out budget mobiles, which have narrowed the technology gap with its flagship models.

"Budget handsets are increasingly replacing high-end models as well," said Lee Ka-keun, an analyst at KB Investment & Securities CO., in the note.

Shinhan Investment Corp. echoed the view, saying Samsung's operating profit is likely to reach 6.46 trillion won in the third quarter, down 6.4 percent from three months earlier.

It further said Samsung's third-quarter smartphone sales are expected to rise 9.6 percent on-quarter, but the operating profit of the division will plunge 18.1 percent due to fiercer competition.

The brokerage house, however, said Samsung's efforts to expand the mobile dynamic random access memory business and the 20-nanometer production technology will help the chip division post improved earnings of 3.47 trillion won.

Samsung's operating profit from the chip business came to 3.4 trillion won in the April-June period, up 82.8 percent on-year. (Yonhap)