HTC's smartphones, once very popular, have lost their edge over the emergence of rivals such as Apple, Samsung Electronics, and more recently Xiaomi.
The Taiwanese company said its June sales fell to T$2.2 billion ($72 million), from T$6.9 billion a year ago and T$2.45 billion in May.
HTC has recently released new flagship phones but obviously the sales have been lower than expected. And the company's middle-end and entry-level models feature neither new specs nor high performance-price ratio.
Last week, HTC said it plans to slash nearly a quarter of its global workforce - or 1,500 jobs - through layoffs at its factory in Taiwan.
HTC has also sold its Pixel team to Google for $1.1 billion. More recently, the company combined its virtual reality and mobile divisions in an effort to refocus and sold its Vive team to Valve.